Jay-Z has announced plans for an offshoot of his Manhattan nightclub 40/40 in the Barclays Center, the sports arena and entertainment complex due in Brooklyn this fall, and neighbors aren’t happy about it. Barclays, and the Atlantic Yards development project it’s a part of, have been a lightning rod for years in the Prospect Heights, Fort Greene and Downtown neighborhoods. Residents unsuccessfully lobbied to scrap the plans, which include the new 18,200 seat arena for the Brooklyn Nets.